Open-source software has become central to library automation, repository development, and discovery service design, particularly in institutions operating under financial and infrastructural constraints. This systematic literature review examines the use of open-source software in library functioning and services, with emphasis on academic libraries and on evidence relevant to rural and remote settings. The review synthesizes studies on integrated library systems, institutional repositories, digital libraries, discovery services, and service sustainability. Koha emerges as the dominant open-source platform for library automation, while DSpace is the most widely reported platform for repositories and digital libraries (Kampa et al., 2024; Ponelis & Adoma, 2018; Cherukodan et al., 2016; Kampa & Patra, 2020). VuFind appears mainly as a lower cost discovery layer used to integrate catalogues, repositories, and subscribed resources (Roy et al., 2018; Bhowmick & Chakrabarty, 2021). The main drivers of adoption are lower total cost of ownership, freedom from vendor lock-in, local customization, interoperability, and alignment with open access values (Kampa & Kaushik, 2019; Choi & Pruett, 2019; Ahammad et al., 2024b). Persistent barriers include weak documentation, limited technical expertise, poor internet and power infrastructure, migration burdens, and uneven institutional support (Kampa et al., 2024; Bwalya & Akakandelwa, 2021; Shehata et al., 2021; Hussain & Rafiq, 2024). Evidence on rural and remote libraries is much thinner, but available studies suggest that the same barriers become more severe in low-resource contexts (Chauhan & Singh, 2012; Oyelude, 2025). The review concludes that open-source software is well established in academic library practice, but its long-term sustainability depends less on software freedom alone than on staffing, governance, documentation, and local technical capacity.